Ubuntu boots in a black window

Hello everybody, I'm a newbie and here's my problem: I installed Ubuntu, so I installed the official ATI drivers but the 3D acceleration wasn't running ok. Then I installed the fglrx following the instructions found in https://help.ubuntu.com/community/BinaryDriverHowto/ATI
#head-5ead174a0b3294527486cd4d71ded66b40003f25 My problem is that when the system boots the monitor is turned off. I can change the session with control+alt+F* but F7 is allways whith the monitor turned off.Anyway, I can insert an user (enter) and the password (enter) so the session is correctly initiated. I can also change the resolution and everything works OK (even the 3D acceleration!), but when I close the session or I try to change the user, the monitor is turned off again and the GDM doesn't work ok. I reinstalled the GDM but the problem continues. I red this post http://www.ubuntux.org/help-ubuntu-6-graphical-login-not-working but it didn't resolved my problem. Should I reinstall Ubuntu? Help me please. Thanks everybody.

A possible solution